Alloys of platinum are used in the jewelry art for the fabrication of settings for precious and semi-precious gemstones. Desired properties, as recognized by the present inventor, include surface whiteness, malleability, strength, durability along with tarnish- and corrosion-resistance and ease of fabrication. The prior art includes alloys with one or more of these characteristics, but not an alloy possessing all of them.
For example, Japan Kokai Tokkyo Koho JP 62130238 A2, published Jun. 12, 1987 (Chem. Abstr. 108:99467), discloses an alloy containing Pt 85-95%, Si 1.5-6.5%, and Pd, Cu, Ir, Au, Ag, Ni, Co and/or Rh for the balance. This alloy has a white platinum color useful in jewelry such as rings, tiepins and watch cases.
Japan Kokai Tokkyo Koho JP 03100159 A2, published April 25, 19U 1 (Chem. Abstr. 116:45112), discloses a metal combination that exhibits a bright black finish rather than a desirable enhanced white finish. The composition of the reference includes: Pt, Rh 3-15%, and/or Ru and .ltoreq.15% of Pd, Ir, Os, Au, Ag, Cu and/or Ni. These materials are heated in air or an oxidizing atmosphere at temperatures below the melting point of the alloys and then quenched in air, water or oil to generate a bright black finish.
Japan Kokai Tokkyo Koho JP 02043333 A2, published Feb. 1 1990 (Chem. Abstr. 113:63801), provides an alloy useful in jewelry manufacture containing Pt 80-98%, Re 0.5-10%, Pd 1-19% and Ru, Rh and/or Ir 0.05-3%, which is said to have improved hardness and castability.
Tucillo (U.S. Pat. No. 3,767,391) discloses a tarnish-resistant alloy useful in cast or wrought dental work and in the manufacture of jewelry, which comprises 47% gold, 9-12% Pd, and the balance silver and copper. Due to the presence of gold, Tucillo's alloys are primarily yellow in coloration and not white.
Japan Kokai Tokkyo Koho JP 07011362 A2, published Jan. 13, 1995 (Chem. Abstr. 122:271622), discloses alloys useful in jewelry applications with Pd.gtoreq.80%, Co 1-5% and Pt 5-15% which are said to have high hardness, formability and corrosion resistance, and do not require coatings.
It is generally known to plate platinum (Pt) with rhodium (Rh) to achieve a desired appearance for jewelry. However, a plated platinum coating is not durable over time, i.e., the coating wears off, and the base material does not exhibit the desired properties noted above, presenting poor appearance after such wear.
None of the above prior art alloys meets the requirements of stable, long-term whiteness, strength, and malleability, combined with ease of preparation. The present inventor recognizes a need for metal alloy compositions for use in jewelry which retain exceptional whiteness without requiring a rhodium plating process while providing desirable mechanical properties for jewelry.